Hybrid vehicles incorporating an electric motor as a driving source in addition to an internal combustion engine are known. In such hybrid vehicle, when the vehicle speed is low, for example, the internal combustion engine is stopped and only the electric motor can be used for running. The internal combustion engine is started when the accelerator position becomes larger, for example. It is desired to drive the internal combustion engine with high thermal efficiency.
Japanese Patent Laying-Open No. 2006-94626 (PTL 1) discloses in paragraph 0034 and the like that an engine is driven when requested power that is set based on the accelerator position is equal to or greater than a threshold value. Japanese Patent Laying-Open No. 2006-94626 also discloses in paragraph 0036 and the like that the engine is operated based on the requested power that is reset to increase by a compatible value which is set to increase overall efficiency.